Bit weighting alignment in a display device

ABSTRACT

The disclosed embodiments relate to a method and apparatus to align bit weights in a display device. There is provided a method for calibrating light output in a display device, the method comprising: displaying a first video pattern, the first video pattern comprising a first set of pixels divided into a first subset of pixels and a second subset of pixels, the first subset of pixels having a first intensity level, the second subset of pixels having an intensity level corresponding to a fully off state; measuring a first light output value associated with the first video pattern; displaying a second video pattern, the second video pattern comprising a second set of pixels, each of the second set of pixels having a second intensity level corresponding to a fraction of the first intensity level, the fractional value of second intensity level being determined so that a second light output value associated with the second video pattern is intended to equal the first light output; measuring the second light output value; and adjusting the fractional value of the LSB to converge the second light output value with the first light output value.

FIELD OF THE INVENTION

The present invention relates generally to digital imaging systems. Morespecifically, the present invention relates to a system and method foraligning bit weights in digital imaging systems that implement pixelshifting technology.

BACKGROUND OF THE INVENTION

This section is intended to introduce the reader to various aspects ofart which may be related to various aspects of the present inventionthat are described and/or claimed below. This discussion is believed tobe helpful in providing the reader with background information tofacilitate a better understanding of the various aspects of the presentinvention. Accordingly, it should be understood that these statementsare to be read in this light, and not as admissions of prior art.

A common problem inherent with digital imaging systems is that they arelimited in the number of bits that can be displayed. In other words,their bit depth is finite. This limitation in the number of bits is aresolution limitation causing contouring in the displayed images.Essentially, the number of colors that may be displayed, as well as therange of light intensity, is limited, precluding the displaying ofsmoother images. In order to increase the resolution of the imagedisplay systems the bit depth needs to be increased.

In digital micromirror devices (“DMD”) using pixel shift technology, oneparameter limiting the bit depth is the value of the least significantbit (“LSB”). The LSB represents the minimum amount of time that a pixelcan be switched on for a given frame of video. One technique to achievebetter bit depth or to increase the number of bits that can be displayedis to create fractional bits. Parameters such as light intensity may becontrolled over time intervals shorter than the time represented by theLSB by, for example, attenuating the light source during the interval anLSB is displayed. However, once these fractional bits are achieved theymust be scaled to the LSB in order to obtain a proper video to lighttransfer curve. Without proper scaling or calibration of the fractionalbits, contouring within the image displayed may persist even with theincrease in bit depth. Therefore, a system and method for calibrating orproperly scaling these fractional bits to the natural LSB is needed.

SUMMARY OF THE INVENTION

Certain aspects commensurate in scope with the disclosed embodiments areset forth below. It should be understood that these aspects arepresented merely to provide the reader with a brief summary of certainforms the invention might take and that these aspects are not intendedto limit the scope of the invention. Indeed, the invention may encompassa variety of aspects that may not be set forth below.

The disclosed embodiments relate to a system and method for bitweighting alignment in a display device. A method for calibrating lightcomprises: displaying a first video pattern, the first video patterncomprising a first set of pixels divided into a first subset of pixelsand a second subset of pixels, the first subset of pixels having a firstintensity level, the second subset of pixels having an intensity levelcorresponding to a fully off state; measuring a first light output valueassociated with the first video pattern; displaying a second videopattern, the second video pattern comprising a second set of pixels,each of the second set of pixels having a second intensity levelcorresponding to a fraction of the first intensity level, the fractionalvalue of second intensity level being determined so that a second lightoutput value associated with the second video pattern is intended toequal the first light output; measuring the second light output value;and adjusting the fractional value of the LSB to converge the secondlight output value with the first light output value.

BRIEF DESCRIPTION OF THE DRAWINGS

Advantages of the invention may become apparent upon reading thefollowing detailed description and upon reference to the drawings inwhich:

FIG. 1 is a block diagram of an exemplary digital imaging system inaccordance with embodiments of the present invention;

FIG. 2 is an exemplary representation of light output in accordance withembodiments of the present invention;

FIG. 3 is an exemplary pixel shift video pattern in accordance withembodiments of the present invention;

FIG. 4 is an exemplary pixel shift video pattern in accordance withembodiments of the present invention; and

FIG. 5 is a flow chart illustrating an exemplary technique for bitweighting in accordance with embodiments of the present invention.

DETAILED DESCRIPTION

One or more specific embodiments of the present invention will bedescribed below. In an effort to provide a concise description of theseembodiments, not all features of an actual implementation are describedin the specification. It should be appreciated that in the developmentof any such actual implementation, as in any engineering or designproject, numerous implementation-specific decisions must be made toachieve the developer's specific goals, such as compliance withsystem-related and business-related constraints, which may vary from oneimplementation to another. Moreover, it should be appreciated that sucha development effort might be complex and time-consuming, but wouldnevertheless be a routine undertaking of design, fabrication, andmanufacture for those of ordinary skill having the benefit of thisdisclosure.

Referring to FIG. 1, a block diagram of an exemplary digital imagingsystem in accordance with one embodiment of the present invention isshown and generally designated by the reference numeral 10. The digitalimaging system 10 comprises a light engine 12 that shines or directslight to an imaging system 14. In one embodiment the light engine 12 mayinclude a metal halide lamp, such as an ultra high performance (“UHP”)lamp, configured to shine white light.

The imaging system 14 may be a digital micromirror device (“DMD”) or aliquid crystal device (“LCD”). In the case of a DMD device, the imagingsystem may comprise up to one-half million micromirrors or more. Themicromirrors are mounted on microscopic hinges that are electricallyactuated to tilt the micromirrors between an “on” position and an “off”position. Each micromirror represents a pixel displayed on a screen 20.The minimum time a pixel can be switched on for a given frame of videois commonly referred to as an LSB.

A projection lens assembly 16 controlled by a modulator 18 receiveslight that passes through or is reflected from the imaging system 14 anddirects it to the screen 20. The modulator 18 and the projection lensassembly 16 enable the image display unit to implement pixel shifttechnology. In pixel shifting, a single pixel may be displayed atmultiple positions on the screen 20 by adapting the modulator 18 toslightly tilt a projecting lens along an axis. The movement of thepixels is imperceptible to a human eye due to visual persistence. Thus,a single pixel appears to be multiple pixels and the pixel shiftingeffectively multiplies the number of pixels available to the digitalimaging system 10.

To perform pixel shifting, a video control system 24 may coordinate themovement of the lens through the modulator 18. With a single modulator18 at least two positions may be achieved for a single pixel. Forexample, the lens may direct pixels to a certain location on the screen20. The modulator 18 then manipulates the lens to direct the pixels to asecondary position on the screen 20 and subsequently back to theoriginal position. The procedure is repeated so rapidly that a human eyeis unable to detect the movement between the two positions and, asexplained previously, the pixel shift technology effectively increasesthe resolution of image displayed on the screen.

The light passing through the projection lens assembly 16 is directedonto the screen 20 as an image seen by viewers. The image display unit10 may be designed to provide an overscan, wherein light is projected toan area greater than that visible to users on the screen 20. Forexample, light may be projected to areas behind a bezel (not shown) ofthe screen. A photodiode assembly 22 may be situated to receive thislight without influencing the image displayed on the screen 20.

The photodiode assembly 22 is configured to detect the amount of lightoutput from the light source 12 in a given video frame. Upon receivinglight from the projection lens assembly 16, the photodiode assembly 22produces a voltage corresponding to the light output. The voltage isconverted to a corresponding digital signal and directed to the videocontrol system 24.

The video control system 24 controls images that are displayed on thescreen 20. Among other things, as described above and as shown, thevideo control system controls the light source 12, the modulator and theimaging system 14 to produce the images on the screen 24. In controllingthe light source 12, the video control system 24 controls the lightoutput intensity. Specifically, it may decrease the intensity of thelight output to achieve a fractional LSB value. Additionally, it mayfine tune the light output of the light source 12 in order to properlyscale a fractional LSB to a natural LSB value.

Returning to the photodiode assembly 22, it communicates with the videocontrol system 24. Specifically, the photodiode assembly 22 providesfeedback to the video control system 24 in the form of a digital signalcorresponding to the amount of light output in a given frame of video.The video control system 24 compares the values of digital signalsreceived and then determines whether to increase or decrease the amountof light output by light engine 12 when displaying a fractional LSB, aswill be discussed in greater detail below.

Turning now to FIG. 2, an exemplary representation of light output inaccordance with embodiments of the present invention is displayed and isgenerally designated by the reference numeral 26. More specifically, thelight output shown is relative to a full LSB, the full LSB represents100% output by the light engine. The full LSB is attenuated to achievefractional LSBs having ½ and ¼ the light output of an LSB. The lightoutput of a full LSB is shown by LSB 28, where there is no attenuationof the light. As illustrated, the light is attenuated by one half toproduce a ½ LSB 30 and by three quarters to produce the ¼ LSB 32. Theattenuation of the light output to create fraction LSBs in this manneressentially increases the number of bits available to display an image.After creation, however, the fractional bits must be properly weightedwith reference to a natural LSB to help ensure an accurate lighttransfer curve.

With reference to FIG. 3, an exemplary pixel shift video pattern isshown and is generally designated by the reference numeral 34.Specifically, the pixel shift video pattern 34 comprises an array ofdiamond shaped pixels having a first pixel position 36 a and a secondpixel position 36 b that is shifted from and partially superimposed uponthe first pixel position 36 a.

In FIG. 3, while the pixels are located in a first pixel position 36 athey have a value of one, the one representing the value of one fullLSB. Alternatively, while the pixels are located in a second pixelposition 36 b the pixels have a value of zero, the zero representingzero LSB or no light being directed to the screen. The result of thepixel shift video pattern 34 is that one half of the total pixels makingup the video frame have an LSB value of one and the other half have avalue of zero. Thus, the total light output of pixel shift video pattern34 is one-half LSB. The total light output of the video pattern can bemeasured by the photodiode assembly 22. This natural LSB value may becompared with the fractional bit weight values of fractional pixels, asdiscussed below.

FIG. 4 is an exemplary pixel shift video pattern in accordance withembodiments of the present invention and is generally designated by thereference numeral 38. The pixel shift video pattern 38 is identical tothe pixel shift video pattern 34 of FIG. 3 in all respects except all ofthe pixels making up the video frame have a light output value ofone-half LSB. Specifically, the pixels while in the first pixel position36 a have a value of one-half LSB and all of the pixels in the secondpixel position 36 b also have a value of one-half LSB. The total lightoutput of the pixel shift video pattern 38 should equal the one-half LSBof video pattern 34. The total light output from pixel shift videopattern 38 may be measured by the photodiode assembly 22, which producesa voltage level corresponding to the amount of light it receives. Thevoltage level is converted to a digital signal and sent to the videocontrol system 24.

The video control system 24 compares the one-half LSB value producedfrom the video pattern 38 with the natural one-half LSB value obtainedfrom the pixel shift video pattern 34 represented in FIG. 3. Acomparison of these two pixel shift video patterns enables the videocontrol system 24 to adjust the light output from the light source 12 tocalibrate the fractional bits with the natural LSB. The calibrationentails converging the value of video pattern 38 to the value of thepixel shift video pattern 34. This weighting of the fractional bits tothe natural LSB helps ensure a smoother image and reduces contouring.

Once the one-half LSB light output level is calibrated or properlyscaled with the natural LSB, the procedure may be repeated to properlyscale other fractions of the LSB such as one fourth LSB. For example, toscale the one-fourth LSB, the calibrated one-half LSB would be used inthe place of one LSB in the video pattern 34 of FIG. 3 and theone-fourth LSB would replace the one-half LSB of the video pattern 38 ofFIG. 3. All of the other procedures remain as described above.

Turning to FIG. 5, a flow chart illustrating an exemplary technique forbit weighting in accordance with embodiments of the present invention isshown and generally designated by reference numeral 40. Specifically,the flow chart shows the steps of ensuring proper bit weighting offractional bits in an image display device using pixel shift technology.In one embodiment, the technique 40 may be performed upon start up ofthe image display unit 10. Alternatively, the video control system 24and the light engine 12 in conjunction with the photodiode assembly 22may perform the technique 40 on the fly or while in operation to ensurecontinued proper fractional bit scaling.

As indicated by block 42, the technique 40 may begin when the device isturned on. Initially, video pattern 34 is made wherein pixels aredisplayed in the first pixel position 36 a with a light output of oneLSB, then pixels are displayed in the second pixel position 36 b withzero LSB or in a fully off state. As indicated by block 48, a voltageoutput may be read from the photodiode at this time. This voltage outputis representative of the total light output of the pixel shift videopattern 34.

Next, video pattern 38 is made, wherein pixels may be displayed in theirfirst pixel position 36 a with one-half LSB and then shifted anddisplayed in their second pixel position 36 b, again with one-half LSB.A voltage may be read from the photodiode assembly 22 as indicated byblock 54. This voltage represents the total light output of the pixelshift video pattern 38, where all of the pixels display a one-half LSB.This voltage level is compared with the voltage level of the pixel shiftvideo pattern 34 which was obtained earlier. If the voltage levels donot match, the video control system 24 adjusts the light output of thelight engine 12 to converge the voltage level represented in block 54with the voltage level represented in block 48. For example, if thevideo pattern 38 produced a higher voltage level than the video pattern34, the light output of the light source 12 should be further attenuatedwhen displaying a fractional LSB. The technique is repeated until thevoltage levels match and the bit weight of the fractional bits arescaled to the natural LSB. When the voltage levels are sufficientlyclose, the calibration ends.

As previously described, technique 40 may be performed upon an initialstart up, or during use. Additionally, this calibration or scaling ofthe fractional bits may be performed in the factory before the imagedisplay unit is shipped to consumers.

While the invention may be susceptible to various modifications andalternative forms, specific embodiments have been shown by way ofexample in the drawings and described in detail herein. However, itshould be understood that the invention is not intended to be limited tothe particular forms disclosed. Rather, the invention is to cover allmodifications, equivalents, and alternatives falling within the spiritand scope of the invention as defined by the following appended claims.

1. A method for calibrating light output in a display device, the methodcomprising: displaying a first video pattern, the first video patterncomprising a first set of pixels divided into a first subset of pixelsand a second subset of pixels, the first subset of pixels having a firstintensity level, the second subset of pixels having an intensity levelcorresponding to a fully off state; measuring a first light output valueassociated with the first video pattern; displaying a second videopattern, the second video pattern comprising a second set of pixels,each of the second set of pixels having a second intensity levelcorresponding to a fraction of the first intensity level, the fractionalvalue of second intensity level being determined so that a second lightoutput value associated with the second video pattern is intended toequal the first light output; measuring the second light output value;and adjusting the fractional value of the LSB to converge the secondlight output value with the first light output value.
 2. The method ofclaim 1, wherein the first intensity level corresponds to a leastsignificant bit (“LSB”) of a DMD array and the second intensity levelcorresponds to an LSB value of one-half.
 3. The method of claim 1,wherein the second subset of pixels are shifted in position relative tothe first subset of pixels.
 4. The method of claim 1, wherein the firstintensity level corresponds to a one-half LSB value of a DMD array andthe second intensity level corresponds to an LSB value of one-fourth. 5.The method of claim 1, wherein a light source is adapted to beattenuated to achieve multiple intensity levels.
 6. The method of claim1, wherein the first and second values correspond to voltages producedby photodiodes.
 7. The method of claim 1, wherein implementation of themethod occurs periodically to help ensure continual proper lighttransfer curve.
 8. A video unit, comprising: a light engine thatproduces a light output; an imaging system that receives the lightoutput and processes the light output to create a processed lightoutput; a projection lens assembly that receives the processed lightoutput and directs the processed light output to a screen; a modulatorenabled to tilt the projection lens assembly along an axis; a photodiodeassembly configured to receive light directed toward the screen andproduce a first voltage according to a first video pattern and a secondvoltage according to a second video pattern; and a video control systemconfigured to adjust the light output of the light engine to convergethe second voltage with the first voltage.
 9. The video unit of claim 8,wherein the imaging system is a digital micromirror device.
 10. Thevideo unit of claim 8, wherein the modulator enables the unit to shiftpixel position on the screen to create subsets of pixels for the firstand second video patterns.
 11. The video unit of claim 8, wherein thefirst video pattern comprises a first subset of pixels with an intensitylevel of one LSB of a DMD array and a second subset of pixels having anintensity level corresponding to a fully off state; and wherein thesecond video pattern comprises pixels having an intensity level ofone-half of an LSB of a DMD array.
 12. The video unit of claim 8,wherein the first video pattern has a first subset of pixels having anintensity level of one-half LSB of a DMD array and a second subset ofpixels having an intensity level corresponding to a fully off state; andwherein the second video pattern has pixels having an intensity level ofone-fourth of an LSB of a DMD array.
 13. The video unit of claim 8,wherein the photodiode assembly is adjacent to the screen, but notvisible to a viewer.
 14. The video unit of claim 8, wherein the firstand second voltage levels are converted to a digital signalcorresponding to their respective voltage levels.
 15. The video unit ofclaim 8, wherein the light engine is adapted to produce an attenuatedlight output corresponding to control signals.
 16. A video unitcomprising: means for creating a first video pattern having pixels in afirst position with a first intensity level and shifting the pixelsrelative to the first position to a second position and having anintensity level corresponding to an off state in the second position;means for creating a second video pattern having pixels in a first andsecond position wherein the value of the pixels of the second videopattern have an intensity level corresponding to a fraction of the firstintensity level; means for measuring a value corresponding to the lightoutput of the first and second video patterns and; means for comparingthe value of the second video pattern with the first video pattern; andmeans for adjusting the second video pattern so that the valuecorresponding to the light output of the second video pattern convergesto the value of the first video pattern.
 17. The video unit of claim 16,further comprising means for producing pixels with a light intensityequal to an LSB value of a DMD array.
 18. The video unit of claim 16,further comprising means for producing pixels with a light intensityequal to one-half of an LSB value of a DMD array.
 19. The video unit ofclaim 16, further comprising means for producing pixels with a lightintensity equal to one-fourth of a LSB value of a DMD array.
 20. Thevideo unit of claim 16, further comprising means for fine tuning thelight output of a light engine to properly scale fractional bits.